getAttributeType and getPropertyType should default to HTML namespace, not ""

[smaug----]

Currently the algorithms oddly change empty string to HTML namespace.
That prevents using the methods with elements which are in "" namespace
(whether or not that is actual useful).
But if the methods just defaulted to HTML namespace, then one could still explicitly pass "".

Even better would be to remove both methods, since it is unclear if they are needed.

[koto]

+1 to removing them, after confirming they see no significant enough usage.

[lukewarlow]

Based on discussion in #384 these potentially aren't going to be removed so it would be good to get clarification on the original question